1. Field of the Invention
This invention relates to a control valve with displacement-compensating seal apparatus which is useful for handling abrasive fluids.
2. Information Disclosure Statement
Pressurized reactors have been used at elevated temperatures in the oxidation of biomass/powdered activated carbon slurry for carbon regeneration, or for materials conditioning, such as thermal conditioning of wastewater sludges. Inert solids accumulation in the lower portion of the reactor necessitates their removal for proper system operation. The removal of solids during system operation requires a controlled, intermittent transfer of an abrasive slurry from a heated, pressurized vessel to ambient temperature and pressure conditions. A conduit fitted with a pressure control valve is used for this controlled, intermittent transfer of the slurry from the reactor to a discharge receiving vessel. The above described process is often termed a blowdown cycle for solids removal from a wet oxidation pressure reactor.
The removal of solids from a wet oxidation reactor through a pressure control valve is described by Bauer in U.S. Pat. No. 4,139,461 and No. 4,217,218. The hot slurry from the reactor is mixed with cold water prior to traversing the pressure control valve to reduce wear on that valve.
Berrigan et al. in U.S. Pat. No. 4,749,492 disclose removing a blowdown slurry of grit ash and regenerated powdered activated carbon from a wet oxidation reactor through a valve, then diluting the slurry with water for subsequent recovery of powdered activated carbon.
A receiving vessel or blowdown pot for collecting a slurry from a wet oxidation reactor is disclosed by Meidl et al. in U.S. Pat. No. 4,620,563. The slurry enters the blowdown pot from the reactor through a pressure control valve.
Passing a pressurized, hot slurry from a reactor to a receiving vessel results in high velocity, abrasive fluid traversing the pressure control valve, as well as the generation of large volumes of water vapor or steam as the slurry reaches atmospheric temperature and pressure. The pressure control valve is best located close to the receiving vessel to minimize wear on any piping connecting the control valve and receiving vessel. The receiving vessel contains liquid water to cushion the slurry transfer and concurrent water vaporization. To retain the water vapor, steam and solids within the receiving vessel as the slurry reaches ambient conditions, the pressure control valve is best securely fastened to the receiving vessel. The intermittent nature of the operation of this transfer system results in thermal expansion and contraction of the piping and valves between the pressurized vessel and the receiving vessel. To maintain the integrity of the connection between the pressure control valve and the receiving vessel, and to prevent overstressing the piping and equipment connections, a so-called expansion loop of piping is placed between the pressurized vessel and the pressure control valve to compensate for and absorb the thermal expansion of the system. The expansion loop is designed with several bends in the piping, resulting in areas where solids from the slurry may collect and obstruct the flow through the loop. A direct run of piping would help solve the plugging problem, but this reduces piping flexibility and increases stress in the piping and equipment connections to beyond acceptable levels due to thermal expansion.
Further, the pressure control valve must withstand internal pressures up to 7,584 KPa (1100 psig) and temperatures up to 260.degree. C. (500.degree. F.) as well as high velocity slurry particles impacting the valve seat. The abrasive nature of the depressurizing slurry within commonly available pressure control valves results in severe erosion problems, even though the valve seats and plugs can be made of erosion-resistant materials such as ceramics. The high velocity depressurizing slurry generated within the pressure control valve can wear away other non-ceramic portions of the pressure control valve body, requiring frequent replacement of the whole valve unit.
To overcome the plugging problem associated with the expansion loop and the erosion problem of the abrasive, high velocity, depressurizing slurry, a new pressure reducing control valve with displacement compensating external seal has been invented.